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Influenza virus…read more

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Influenza, commonly known as "the flu", is an infectious
disease caused by RNA viruses of the family
Orthomyxoviridae, the influenza viruses.
The virus particle is 80­120 nanometres in diameter and
usually roughly spherical.
There are 3 types of flu viruses:
Influenza A : Wild aquatic birds are the natural hosts of
influenza A. Occasionally, these are transmitted to other
species and may then cause devastating outbreaks in domestic
poultry or give rise to human influenza pandemics. These
viruses are the most virulent human pathogens among the 3
influenza types and cause the most severe disease.
Influenza B: This genus has 1 species. It almost exclusively
infects humans and is less common. The reduced rate of
antigenic change, combined with its limited host range,
ensures that pandemics of influenza B do not occur.
Influenza C: This genus has one species, which infects humans,
dogs and pigs, sometimes causing both severe illness and local
epidemics. However, influenza C is less common than the
other types and usually only causes mild disease in children.…read more

Slide 3

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Diagram of the virus
NA ( neuraminidase) is involved in
the release of progeny virus from
Glycoproteins infected cells by cleaving sugars that
­ targets for bind the mature viral particles. Thus
antiviral these proteins are targets for antiviral
drugs. Viral RNA
drugs. They genome ­
are antigens usually single
to which stranded. There
antibodies are usually 7 or
can be raised. 8 pieces of
n) is a lectin
that mediates segmented
the binding of negative sense
the virus to RNA with each
target cells and piece
entry of the containing one
viral genome or two genes
intoLipid membrane
the target which code for
M1 (matrix protein) forms a
cell.which is taken from a protein.
shell to give strength and
the host cell in which
rigidity to the lipid
the virus multiplies.
envelope.…read more

Slide 4

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Influenza viruses bind through
hemagglutinin onto sugars on the
surfaces of epithelial cells, typically in the
nose, throat, and lungs. After the
hemagglutinin is cleaved by a protease,
the cell imports the virus by endocytosis.
Once inside the cell, the acidic conditions
in the endosome cause two events to
happen: First, part of the hemagglutinin
protein fuses the viral envelope with the
vacuole's membrane, then the ion
channel allows protons to move through
the viral envelope and acidify the core of
the virus, which causes the core to
dissemble and release the viral RNA and
core proteins.The viral RNA molecules,
accessory proteins and RNA-dependent
RNA polymerase are then released into
the cytoplasm.
These core proteins and vRNA form a
complex that is transported into the cell
nucleus, where the RNA-dependent RNA
polymerase begins transcribing
complementary positive-sense vRNA .
The vRNA either is exported into the
cytoplasm and translated or remains in
the nucleus. Newly synthesized viral
proteins are either secreted through the
Golgi Apparatus onto the cell surface or…read more

Slide 5

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Negative-sense vRNAs that form the genomes of future
viruses, RNA-dependent RNA polymerase, and other viral
proteins are assembled into a virion. Hemagglutinin and
neuraminidase molecules cluster into a bulge in the cell
membrane. The vRNA and viral core proteins leave the
nucleus and enter this membrane protrusion.The mature
virus buds off from the cell in a sphere of host phospholipid
membrane, acquiring hemagglutinin and neuraminidase with
this membrane coat. As before, the viruses adhere to the cell
through hemagglutinin; the mature viruses detach once their
neuraminidase has cleaved sialic acid residues from the host
cell. After the release of new influenza viruses, the host cell
Because of the absence of RNA proofreading enzymes, the
RNA-dependent RNA polymerase that copies the viral
genome makes an error roughly every 10 000 nucleotides,
which is the approximate length of the influenza vRNA.
Hence, the majority of newly manufactured influenza viruses
are mutants; causing antigenic drift, which is a slow change in
the antigens on the viral surface over time.The separation of
the genome into 8 separate segments of vRNA allows mixing
or reassortment of vRNAs if more than one type of influenza
virus infects a single cell. The resulting rapid change in viral
genetics produces antigenic shifts, which are sudden changes
from one antigen to another. These sudden large changes…read more


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